Ovary

Expression of CCAAT/Enhancer Binding Proteins Alpha and Beta in the Porcine Ovary and Regulation in Primary Cultures of Granulosa Cells

Abstract
The expression of C/EBP and transcription factor mRNAs and proteins was evaluated in porcine ovarian structures during the estrous cycle. C/EBP mRNA was present in antral follicles and significantly increased in healthy corpora lutea (CL), whereas C/EBP mRNA was constitutively expressed in these structures. Both isoforms of C/EBP (42 and 30 kDa) exhibited greater expression in preovulatory follicles and the 42 kDa isoform increased in CL whereas the 30 kDa isoform decreased. All major isoforms of C/EBP (38, 34, and 20 kDa) were expressed, with the 34 and 20 kDa isoforms being more abundant in preovulatory follicles and further increased in CL. The effects of FSH and cyclic AMP analogue on the distribution of C/EBP isoforms were also evaluated in primary cultures of porcine granulosa cells. FSH and 8-Br-cAMP had little stimulatory effect on isoform distribution but cAMP treatment (24 h) tended to decrease the 30 kDa form of C/EBP and the 34 kDa form of C/EBP. The 34 kDa form of C/EBP was decreased by the PKA inhibitor H89 at 4 h (with FSH treatment) and by both PKA and PI3-kinase inhibitors at 24-h treatment. In transfected granulosa cells, FSH and cAMP analogue stimulated a C/EBP consensus sequence-reporter construct that was blocked by H89. These data implicate PKA as the major regulator of C/EBP isoform distribution and C/EBP-mediated transactivation in granulosa cells. The differential expression of specific C/EBP/ isoforms observed in maturing follicles and CL may contribute to changes in follicular cell differentiation and increasing steroidogenic capacity.

Key words: Ovary • Corpus luteum • Cyclic adenosine monophosphate • Follicle-stimulating hormone • Granulosa cells

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